Headed for the Mountains
Join Date: Nov 2004
Location: Victoria, BC, Canada.
Don't actually own commercially made siltarps - I made myself several instead (bought the fabric online from Noah Lamport, cost is about 3$ per square metre + a little bit for the trimmings). I have one nice hexagonal catenary cut one (like a silwing) that is about 3 metres long and 2 metres wide (fits over a hammock), and another larger square one ( 4 x 3 m). I haven't had any problems with durability, and I've used them a fair amount as sun shelters, windblocks and tarps in heavy downpour. They do certainly pack down very small, The little once fits in a stuffsack that is about 10 x 5 x 15 cm, and the larger one maybe 10 x 7 x 20 - though really more like an egg with those dimensions. That is with me just stuffing them into a stuffsack. If I cram it up into the end of a kayak, or down into a backpack or stuffsack, I can get them 2/3 or maybe even 1/2 that size. Couldn't tell you weightwise - though I think the tieout cords weight more than the tarp fabric.... Lighter than the 'normal' scout tarp I had, per area. The scout tarp was fine for 2 people, I imagine it would be fine for 2 people plus dog.
It isn't just a silicone coating - the fabric is essentially soaked in silicone.
It is true that you have to retension them a bit once they get wet, but even when I've done a bad setup and had big pools, I haven't had problems with it soaking through in those places. I've never used the material as a groundsheet, but I've read of other people who have - the major complaint seems to be that it is very slippery and you need to pitch on very flat surfaces or you slip around - haven't heard complains of leakthrough. The fabric is sold (where I bought it anyways) as zero-porosity, and used for braking parachutes on racecard and stuff, and in making the little stuffsacks for the tarps out of it, I deliberately left the seams unsealed (on the bag), otherwise they would get hard to stuff in because of the trapped air - so I imagine they probably are pretty waterproof. They are nice in that they barely soak up any water - just shake them a few times while pitched, everything beads up and rolls off - then stuff it up and good to go.